1. Field of the Invention
The present invention relates to a multimedia server for transferring multimedia data to terminals in response to requests from terminals.
2. Description of the Background Art
In general, as a memory device for storing multimedia data to be used in a video server, a memory device with a capacity larger than that of a conventional memory device for text data is required. However, a memory device such as a semiconductor memory device which enables a high speed access but which also requires a high cost per capacity is not suitable as a storage of multimedia data. Consequently, a memory device such as a magnetic memory device or an optical memory device for which an access speed is not so fast but a capacity is large and a cost is not so high has been often used as a storage of multimedia data.
In addition, in a case of transferring video data and/or speech data to a terminal, a video server is required to have a data supply capability higher than a data reproduction capability of the terminal.
A multimedia server including a video server is required to be capable of responding to many requires from many users immediately, but an access speed of a memory device can be a bottleneck when accesses are concentrated on a particular memory device storing popular multimedia data, and it can lead to a lowering of a performance of a system as a whole. A conventional measure to resolve this problem includes a provision to shorten the access time by caching data in a cache memory with a small capacity but a high access speed, and a provision to provide a plurality of memory devices in parallel to realize a data transfer with a reduced access load on each memory device.
However, in a case of multimedia data such as video data, each data requires a large capacity, so that a cache memory with a large capacity is necessary in order to realize an effective caching, and there is a need to devise a scheme to distribute accesses to different memory devices in a case of providing a plurality of memory devices in parallel.
Moreover, a scheme for handling all requests within a prescribed time period collectively such as a near video-on-demand scheme can avoid a concentration of accesses to a particular memory device to some extent by processing accesses to the identical data collectively, but in this scheme, data transferred from the server are uncontrollable at each terminal, and there is a time lag between a time at which a request is made and a time at which data are provided.
Thus, in a conventional multimedia server, there has been a need to take out the identical multimedia data repeatedly from a memory device having a low access speed. In particular, in a case of the video server, many accesses are often concentrated on a famous video program or a new or topical video program, so that there has been a demand for an efficient scheme to handle many accesses to the identical multimedia data.